There have been widely known DC arc plasmatrons comprising a rod cathode, a nozzle anode having a body member and a central orifice, both electrodes being typically water-cooled, a power supply unit connected to the both electrodes, and a gas system for feeding plasma-forming gas into the inter-electrode space. Such DC arc plasmatrons have been disclosed in U.S. Pat. No. 3,051,639, 1962, by Anderson; U.S. Pat. No. 4,035,684, 1977, by Svoboda et al.; U.S. Pat. No. 4,569,918, 1986 of Ponghis; and U.S. Pat. No. 6,114,649, 2000, by Delcea. In such plasma sources the cathode is typically made of tungsten that, at temperature up to 3200° C., reaches the thermo-ionic emission mode with an erosion rate of about 10−9 g/C. This level of erosion is achieved only in contact with chemically inert plasma-forming gas like argon or nitrogen. Water-cooled anodes are destroyed much more intensively. In particular for copper that is often used to fabricate these parts, the erosion rate reaches 10−6 to 10−5 g/C which in turn limits service time of such plasmatrons to between 10° and 101 hours and results in a high level of plasma contamination with copper vapor and clusters. These factors limit wide use of these plasmatrons for technologic purposes especially in the field of electronics.
U.S. Pat. No. 6,114,649, 2000, by Delcea discloses ring members on the internal surface of the anode orifice. These rings cause circuit vortex to be formed on the internal surface of the anode that attracts arc roots, or spots, fix the length of the discharge and stabilize the discharge parameters. On the other hand, the arc spot mechanism in this situation remains without changes, keeping the anode erosion rate at the aforementioned level (this mechanism includes local melting and overheating of an anode spot and subsequent explosion that induce the metal drop and cluster formation).
U.S. Pat. No. 3,051,639, 1962, by Anderson discloses special refractory metal radial inserts fixed in an anode body member with internal ends of the inserts leveled flat with the anode internal surface. This approach intended to lower the anode erosion rate but its effect turned out to be relatively small because this anode embodiment was also proved unable to change the destructive mechanism of the constricted anode arc spots.
The aforementioned patent, U.S. Pat. No. 3,051,639, discloses a technology of plasma-chemical reformation of hydrocarbon fuel using an annular collector located around the anode orifice. Said collector is provided with external fuel feeding conduits and a plurality of internal circumferentially-disposed openings downstream of the above said refractory inserts; said openings connect said collector with the anode orifice. This technology failed to provide high ability for the process gas activation because heating plasma forming gas in the anode area was non-uniform due to constricted nature of the anode spots. Small sized hot anode spot areas achieved heating for only a small fraction of the total plasma flow. As a result, the effectiveness of plasma-chemistry in the torch was not sufficient.
There is known from all aforementioned patents a method of using the a DC arc plasmatron comprising the steps of selecting suitable technologic gas, switching on water cooling and gas supplying systems to the plasmatron and then exciting arc discharge between its anode and cathode using a high-voltage/high-frequency startup oscillator. This method based on electrical breakdown of the inter-electrode space does not work in vacuum: according to the Paschen law in vacuum the discharge damages the parts like soldered seams, and collects cathode chucks, thin non-cooled elements, etc., that are never designed to be exposed to the action of arc spots.
Analysis of the prior art technologies shows that the technical decisions described in U.S. Pat. No. 3,051,639, 1962, by Anderson are the closest one with respect to the present invention. That is why it was selected as a reference.